Phytophthora nemorosa

Name and publication

Phytophthora nemorosa Hansen and Reeser (2003)

Hansen EM, Reeser PW, Davidson JM, Garbelotto M, Ivors K, Douhan L, and Rizzo DM. 2003. Phytophthora nemorosa, a new species causing cankers and leaf blight of forest trees in California and Oregon, U.S.A. Mycotaxon 88: 129–138 (pg 131).


from Hansen et al. (2003)




refers to the forest setting from which most isolates have been recovered


Type: UNITED STATES, Humbolt County in California, recovered from tanoak (Lithocarpus densiflorus); type specimen (a dried agar culture) deposited in the Oregon State University Mycological Herbarium (OSC 104381) from isolate P-13

Ex-type: culture MYA-2948 (ATCC) from isolate P-13

Sequences for ex-type in original manuscript: P-13 = ITS rDNA AY332651

Ex-type in other collections

MYA-2948 = P-13 = CBS 114870P19600 (WPC), p320, 42C4, CPHST BL 27, 41C4 (Yang)

Molecular identification

Voucher sequences for barcoding genes (ITS rDNA and COI) of the ex-type (see Molecular protocols page)

Phytophthora nemorosa isolate CPHST BL 27 (= P19600 WPC) = ITS rDNA MG865548, COI MH136941

Sequences for selected specimen

Phytophthora nemorosa isolate CPHST BL 167 (= P10288 WPC) = ITS rDNA MG865549, COI MH136942

Sequences for ex-type in other sources
Position in ITS phylogenetic tree

Clade 3a

Morphological identification

Colonies and cardinal temperatures

Colony morphology on V-8 agar with rosette pattern, potato dextrose agar with no distinct pattern, and malt extract agar with slow growth. Minimum for growth 3°C, optimum 15–20°C, maximum 21°C.

Conditions for growth and sporulation

Chlamydospores and hyphal swellings are observed in old 10% soil solution water cultures.

Asexual phase

Sporangia semipapillate; caducous with medium to long pedicel (5–20 µm L); ellipsoid, ovoid, obpyriform, obovoid, obturbinate, (27–64 L x 19–45 W µm), but predominantly ovoid or irregular in shape (asymmetrical, kidney-shaped); originated in simple sympodial or branched sporangiophores. Hyphal swellings globose, sub-globose, ellipsoid and intercalary, many times with radiating hyphae and often produced in chains. Chlamydospores globose and sub-globose (18–41 µm diam.), terminally, intercalary, or catenulated.

Sexual phase

Homothallic. Oogonia smooth-walled (18–42 µm diam.) occasionally with tapered bases, and may have somewhat wavy walls; antheridia amphyginous (11–21 x 10–15 µm); oospores aplerotic, plerotic, or slightly aplerotic (16–35 µm diam.).

Specimen(s) evaluated

Phytophthora nemorosa ex-type CPHST BL 27, duplicate of P19600 (World Phytophthora Collection), which is a duplicate of ex-type MYA-2948

Hosts and distribution

Distribution: North America (CA, OR)
Substrate: leaves, bark of boles
Disease note: lethal bole canker of oaks, foliar necrosis. It co-occurs with Phytophthora ramorum, but is often associated with a single tree rather than patch mortality (Hansen et al. 2003).
Host: various families, including the Fagaceae Lithocarpus densiflorus (tanoak) and Quercus agrifolia (live oak)

Retrieved January 31, 2018 from U.S. National Fungus Collections Nomenclature Database.

Additional references and links

Fact sheet author

Z. Gloria Abad, Ph.D., USDA-APHIS-PPQ-S&T Beltsville Laboratory, United States of America